code: def test_empty_signals_return_unknown() -> None:  # noqa: D
      result = solver.solve_column(column, [])
  
      assert result.type_node == InferenceSignalType.UNKNOWN
      assert len(result.reasons) == 0
      assert len(result.problems) == 2
  
file_path: metricflow/metricflow/test/inference/solver/test_weighted_tree.py
imports: from __future__ import annotations
  from metricflow.dataflow.sql_column import SqlColumn
  from metricflow.inference.models import InferenceSignal, InferenceSignalConfidence, InferenceSignalType
  from metricflow.inference.solver.weighted_tree import WeightedTypeTreeInferenceSolver
label_desc: Use image node_id 1 for calling a global function with example usage: test_empty_signals_return_unknown() without return types